Weak Spark

[Todd Phenneger]

Ok guys,
  Sunny Day in Seattle again.  (FINALLY)  so I went out to the
4ktq to troubleshoot a little more.  I went through the Coil
testing procedure in the Bently and on SJM's website.
    http://www.sjmautotechnik.com/nostart.html#switch
is the link to the page I was referencing.
  So, as per SJM and Bently, I have 12v at the ECU, both ECU
grounds are good.  All engien groudns are good.  Some doubled up
for backup.   As per the check for the Coil and Output stage
here are my finding.
1) I am not able to read the .2v across the Ign Booster
transistor connector while cranking.  My MM Gauge does fluctuate
though as if its reciving some sort of signal so I'm guessign
that it is just not fast enough to register the Voltage.  Only
way to know for sure is to hook up an LED test light I suppose.
I do register .2v at that connector when the ignition is ON
however, but as soon as I crank it fluctuates.
2) While Cranking Voltage at ECU is 10.2v  Thats within Spec.
3) Voltage at Coil is 12v and while cranking is 9.9 - 10v. 
Again within spec.  
4) Coil resistance checks as per bently are within Spec.  Coil
has also been swapped with known good coil.

What gives.  The coil checks out as fine.  The plug wires,
rotor, cap are all replaced.  The ECU "appears" to be sending a
good signal to the coil, and the coil has 12v power.  So why the
heck do I get no spark or weak spark?
  Oh yea, I dumped codes after cranking and get nothing.  Also,
resistance of wire from ECU to Coil checks out Ok.  8-9 ohms I
believe.
Thanks
  Todd


--- SJ <syljay at optonline.net> wrote:
> Have you checked the Hall Effect sensor in the distributor?
> There was a thread on how it works not too long ago.
> 
> Bentley has the procedure for checking it.
> 
> The basic system works like this.
> Hall effect sensor------>Ign ctrl unit----->ign
> coil--->distributor
> There is also a Ignition Booster module that has inputs and
> outputs to the
> Ign ctrl unit.
> I'm not sure what the function of the Booster is, maybe
> amplify the Hall
> effect sensor output.
> 
> Weak spark, usually means weak input current to the coil. Or
> high resistance
> in the coil.
> You have changed the coil, so that leaves weak input current
> to the
> coil(primary current).
> 
> Hall effect sensor works like a light switch . .on-off-on-off
> 
> The tail end of the Ign ctrl unit is basically a relay, it is
> activated by
> the Hall effect sensor and it shuts on and off 12V power to
> the Coil.
> 
> I've heard guys talk about turbocharged cars having a timing
> reference on
> the flywheel. I think when the engine is starting, the ign crt
> unit uses
> this to control the ign coil. After the engine starts, control
> is given to
> the Hall effect sensor. Not sure about this function.
> 
> Hope I gave you some leads to follow up on.
> 
> SJ
> 85 Dodge PU, D-250, 318, auto
> 85 Audi 4k - - sold but still on the road
> 88 Audi 5kq
> 90 Audi 100q
> 
> 
> 


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